Hydrophobicity Tuning in Isostructural Urchin-Shaped Covalent Organic Framework Nanoparticles by Pore Surface Engineering for Oil–Water Separation

Accidental oil spills have released millions of barrels of petroleum hydrocarbons in oceans worldwide, causing severe damage to marine and coastal ecosystems. Materials to clean up these oil spills are therefore in high demand. Here, we report the rapid, scalable microwave-assisted synthesis of two isostructural imine-linked covalent organic frameworks (COFs; TAB-DFP and TAB-MPPD) from 2,6-diformylpyridine (DFP) or 4-(4-(methylthio)­phenyl) pyridine-2,6-dicarbaldehyde (MPPD) and tris­(4-aminophenyl) benzene (TAB) building blocks. The morphology, hydrophobicity, and hydrophilicity of the materials were changed by surface modification. The TAB-DFP COF exhibited a spherical sea urchin-like morphology and was hydrophilic in nature. In contrast, the TAB-MPPD COF exhibited a bowl-shaped hollow spherical morphology. Incorporation of a thioanisole moiety into the structure of DFP resulted in high hydrophobicity with a contact angle of 155 ± 2°. Thus, the TAB-MPPD showed excellent oil removal performance (>500 wt %) for various types of oils. The adsorbed oil could be desorbed by simply washing with ether, and the material could be reused beyond 10 consecutive cycles without any significant decrease in oil removal capacity.

全球海洋因意外溢油事故已累计释放数百万桶石油烃类物质，对海洋及沿岸生态系统造成严重破坏，因此溢油清理材料的市场需求极高。本研究报道了一种快速、可规模化的微波辅助合成策略，以2,6-二甲酰基吡啶（2,6-diformylpyridine，DFP）或4-(4-(甲硫基)苯基)吡啶-2,6-二甲醛（4-(4-(methylthio)phenyl) pyridine-2,6-dicarbaldehyde，MPPD）与三(4-氨基苯基)苯（tris(4-aminophenyl) benzene，TAB）为构筑单元，合成了两种同构的亚胺连接共价有机框架（covalent organic frameworks，COFs；分别命名为TAB-DFP与TAB-MPPD）。通过表面改性可调控该类材料的形貌、疏水性与亲水性。TAB-DFP COF呈现球形海胆状形貌，本征亲水性良好。与之相反，TAB-MPPD COF呈现碗状空心球形形貌。将苯甲硫基（thioanisole）基团引入DFP的分子结构后，所得材料可获得高疏水性，接触角可达155 ± 2°。因此，TAB-MPPD对多种类型的油品均展现出优异的除油性能（吸附量超过500重量百分比）。吸附的油品仅需通过乙醚洗涤即可实现解吸，且该材料可连续循环使用10次以上，除油性能无显著下降。